Cataracts are currently the leading cause of blindness among adults in the United States. A cataract is a clouding of a part of the eye known as the crystalline lens. Although cataracts result from many conditions, the most frequent cause is the natural aging process. Most people develop some clouding of the lens after the age of 60. About 50 percent of Americans ages 65 to 74 have cataract, and about 70 percent of those age 75 and over have it. As there are growing numbers of elderly in the United States, the incidence of cataracts is increasing. Other causes of cataracts may include injury, chronic eye disease, and other system-wide diseases such as, diabetes.
Surgery to remove the diseased crystalline lens is the only effective treatment for cataract. Neither diet nor medications have been shown to stop cataract formation. Cataract surgery is now a frequently performed operation in most parts of the world. More than 1.5 million cataract procedures are performed every year, and, in the majority of those cases, the diseased tissue is replaced with an artificial device known as an intraocular lens implant. This surgery is very successful in restoring vision—more than 95 percent of people who have a cataract removed have no complications and end up with better vision. Many people report not only better vision but also a reduction in the power of their lens prescription and improvements in their overall quality of life after the operation.
Presbyopia, a condition in which the natural lens of the eye becomes thicker and less flexible, is also a symptom of the natural aging process. Patients of presbyopia generally lose the ability of ocular focus due to lack of accommodation ability of the natural lens. Replacement of the natural crystalline lens with an artificial intraocular lens is an emerging treatment for patients with presbyopia.
Intraocular lenses for cataract lens replacement surgery and presbyopia correction surgery differ widely in their physical appearance and arrangement. Intraocular lenses have been described in U.S. Pat. Nos. 4,254,509, 4,298,996, 4,409,691, 4,424,597, 4,573,998, 4,664,666, 4,673,406, 4,738,680, 4,753,655, 4,778,463, 4,813,955, 4,840,627, 4,842,601, 4,963,148, 4,994,082, 5,047,051, 5,674,282, 6,342,073, 6,387,126, 6,451,056, and U.S. Patent Application Publication No. 2003/0050696.
Two general classes of intraocular lenses—accommodating and non-accommodating—have been developed. Non-accommodating intraocular lenses cannot change shape or move in the eye and, therefore, do not operate in conjunction with the natural accommodation capabilities of the human eye, whereas accommodating lenses do have at least some capability to operate in conjunction with the natural accommodation capabilities of the eye. Accommodation involves relaxation and constriction of the ciliary muscle by the brain to provide the eye with near and distant vision. This ciliary muscle action is automatic and shapes the natural crystalline lens to the appropriate optical configuration for focusing on the retina the light rays entering the eye from the scene being viewed. Ocular mechanics of natural eye accommodation are also governed by zonular ligaments connecting the ciliary muscle to the perimeter of the lens and vitreous material that fills the posterior segment of the eye.
Most non-accommodating intraocular lenses have single focus optics which focus the eye at a certain fixed distance only. Other non-accommodating lenses have bifocal optics which image both near and distant objects on the retina of the eye. The brain selects the appropriate image and suppresses the other image, so that a bifocal intraocular lens provides both near vision and distant vision without eyeglasses. Bifocal intraocular lenses, however, suffer from the disadvantage that each bifocal image represents only about 40% of the available light, and a remaining 20% of the light is lost in scatter.
A common design feature of the available accommodative intraocular lenses is to translate the optic forward in the eye. For example, the accommodating intraocular lens disclosed by U.S. Pat. No. 5,674,282 to Cumming is made of a lens body having a central optical zone or optic and plate haptics extending from diametrically opposite edges of the optic. Ciliary muscle contraction exerts opposing endwise compression forces on the ends of the lens haptics with resultant endwise compression of the lens. Relaxation of the ciliarly muscle causes retraction of the lens. Accommodating intraocular lenses designed to translate the optic forward in the eye fail to address an important feature of natural lens accommodation. That is, natural accommodation benefits considerably from changes in surface curvatures. Available accommodating intraocular lenses fail to possess the capability of undergoing changes in surface curvature. In other words, available accommodating intraocular lenses do not uniformly flex and move or maintain their flexibility with in-growth of fibroblasts around the supporting capsular structure of the eye. Furthermore, available accommodating intraocular lenses are not amenable to removal or replacement of the optical lens because of adhesion of the lens to the capsular/zonular support structure of the eye.
The present invention is directed to overcoming these and other limitations in the art.